Reconsidering macro-artefacts in SETI searches
Introduction
Extraterrestrial civilizations could be expected to construct large amounts of infrastructure, assuming that their technological base is at least equivalent to that of present-day Earth. Searching for this infrastructure falls within the realm of “artefact searches”, a long-established segment of the Search for Extraterrestrial Intelligence (SETI). In this case, large infrastructure would be classified as macro-artefacts.
Recent advances in manufacturing technology and astronomy on Earth could suggest that artefact discovery could be more likely in the future. This paper examines the rationale for constructing macro-artefacts on the part of extraterrestrial civilizations as well as methodologies for detecting them. Although a solid case for searching for macro-artefacts can be presented, the dilemmas of discriminating between natural and artificial phenomena will complicate such searches.
Section snippets
Historical background
Macro-artefacts were considered in some of the earliest studies of extraterrestrial messaging from Earth. Famous examples include a plan by the mathematician Carl Gauss to create geometric patterns in a forest in Siberia [1] and a proposal for a burning ring of kerosene to be deployed in the Sahara desert. These nineteenth-century plans were designed to communicate with putative intelligent life elsewhere in our own solar system.
The development of radio astronomy in the twentieth century
The decline of macro-artefacts
Interest in macro-artefacts in SETI has been relatively minimal in recent years. Scholarly work on the subject is rarely encountered in journals or conferences. This is partially due to the prominence of the “radio paradigm” in SETI, which has predominated for more than half a century. This paper does not seek to attack the “radio paradigm”, and notes its strong technical and economic merits. However, it does propose the addition of a new methodology as a supplement rather than a substitute.
The
Advantages of macro-artefacts
This paper defines a macro-artefact as an artificially constructed object of a scale measured in tens of kilometers or larger. The artefact may be located on the surface of a heavenly body or placed in open space.
Some macro-artefacts could be practical infrastructure used by an extraterrestrial civilization for its own purposes. Others could be constructed for the deliberate purpose of signaling to other civilizations. Thus, the division between the ostensive purposes of macro-artefacts
Practical macro-artefacts
The following is a short list of potential macro-artefacts that could be deployed for practical purposes, meaning that they could be part of the infrastructure of an advanced technological civilization.
Contemporary searches for macro-artefacts
While macro-artefacts have not been a major focus of contemporary SETI searches, it is worth observing that some work has been conducted in this area. This has mostly involved searches for Dyson Spheres using infrared observations from space-based observatories. Dyson Spheres are hypothetical spherical shells constructed around the perimeters of star systems, designed to intercept most of the radiated energy from the star within. A Dyson Sphere constructed around a star system would reduce the
3-D printing of macro-artefacts
In recent years, much attention has been given to the rising technology of 3-D printing, which constructs solid objects. Unlike traditional computer-aided manufacturing, which generally cuts or strips away at sheets or blocks of material, 3-D printing builds up objects incrementally by slowly depositing small amounts of material. 3-D printing can use materials ranging from plastic to metal. It has been used in the construction of rocket thrusters [5]. A 3-D printer has been successfully tested
Macro-artefacts as signals
Section 5 of this paper presented types of macro-artefacts that are not ostensively designed as signals to other civilizations. It is also possible that some macro-artefacts could be deliberately constructed to serve as signals on an interstellar scale. The construction of such signals could be easier to achieve than some of the more complex forms of infrastructure previously discussed in this paper. Some are ideally suited to the applications of 3-D printing mentioned in Section 7 as a
Platonic solids as macro-artefacts
While a sail could be an effective signal, it is also possible to envisage more complex types. One alternative would be the construction of three-dimensional macro-artefacts based on the platonic solids. Platonic solids are structures with regular geometric faces such as triangles, squares and pentagons. They are significant to mathematics, geometry and esthetics.
SETI messaging strategies have frequently emphasized the usefulness of mathematics as a communications medium. It is perceived as
Natural versus artificial
Spatial resolution of macro-artefacts would probably be more conclusive than spectral resolution. Something that looks highly artificial is likely to be artificial. Although spectral resolution is much easier for us at the present time, it carries risks. Natural phenomena could be mistaken for artificial ones, and vice versa.
Diffraction by regular geometric substances is a hallmark of nature. Geometric crystalline structures form naturally and are ubiquitous on Earth. The use of diffraction as
New astrophysical phenomena
A putative macro-artefact discovered through spectral resolution could still be natural, even if it does not neatly conform to the properties of known phenomena. The discovery of pulsars, briefly considered as potential extraterrestrial beacons by some astronomers, is an example. One hypothetical natural phenomenon could be the formation of huge crystalline structures in space. These could be generated in nebulas rich in chemicals. Such structures would require a unique blend of chemistry and
Temporal resolution
The detection of some macro-artefacts could be compromised by the temporal resolution and the integration times of some instruments. This applies to both frequency and spatial resolution. Some artefacts may move too rapidly for proper detection and identification. Doppler effects with regard to the object and the observer could also be significant.
The medium and the message
A macro-artefact signal would probably be low on actual messaging content, and merely designed to attract attention. The principal “message” would be to alert observers to the existence of the advanced technological civilization responsible for constructing the artefact. It is possible that more complex, but less easily detected messages could be transmitted from roughly the same location using different methods at the same time that the artefact is deployed. The strategy could be to “hook”
Conclusions
Searching for macro-artefacts is difficult with our present technology, but should be considered for future SETI searches as astronomical technology improves. It could be performed with very advanced optical telescopes as well as instruments operating in other bands of the electromagnetic spectrum. As with radio and laser searches, controversy will exist over the nature of putative discoveries.
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